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Full text of "Chromosome number and individuality in the genus Crepis"

UNIVERSITY OF CALIFORNIA PUBLICATIONS 

IN 

AGRICULTURAL SCIENCES 

Vol. 2, No. 10, pp. 297-314, plate 53 March 5, 1925 



CHROMOSOME NUMBER AND INDIVIDUALITY 
IN THE GENUS CREPIS 

I. A COMPARATIVE STUDY OF THE CHROMOSOME 
NUMBER AND DIMENSIONS OF NINETEEN SPECIES 

BY 

MARGARET CAMPBELL MANN 

( Contribution from the Division of Genetics, University of California ) 



Because most of the species of the genus Crepis have low chromo- 
some numbers, it offers obvious advantages for the study of comparative 
chromosome relations. The chromosome individuality of certain species 
is very distinct, so much so that it could be used as a diagnostic character 
in specific determination. These facts lead to an inquiry to discover first, 
whether upon careful analysis all species would prove to differ in chromo- 
some individuality, and second, what relations the chromosome groupings 
of different species bear to one another. This question has been previously 
touched upon in several papers by Rosenberg (1909, 1918, 1920) and in 
a recent contribution by Marchal (1920). Rosenberg (1918) called 
attention to the fact that the genus Crepis possesses a great variety of 
chromosome numbers. His summary showed species with 3, 4, 5, 8, 
9, and 20 pairs. In order to determine how such numerical differences 
had arisen within the genus, he measured the chromosomes of a three 
and a four-pair species, capillaris (Reuteriana of Rosenberg) and 
tectorum, respectively, and found, on the basis of measurements of 
homotypic anaphase chromosomes, that three of the chromosomes of 
the two species corresponded accurately in size and that the fourth 
pair of tectorum averaged slightly shorter than the shortest of capillaris. 
He noted that the two shortest chromosomes of capillaris often mate 
later than the other two in p. m. c. and finds associated with this fact 
a tendency toward lagging and irregular division. From these data he 



298 University of California Publications in Agricultural Sciences [Vol. 2 

concluded that the four-pair species have arisen from a three-pair species 
by the fusion of two gametes each of which has received an extra short 
chromosome. Although he did not publish measurements on the two 
five-pair species which he studied (rubra and multicaulis) , he believed 
that both have three of the short chromosomes, and that these types 
have originated by a repetition of the process which gave rise to the 
four-pair types: In his 1920 contribution he changes his count in biennis 
from twenty to twenty-one pairs and concludes that it represents the 
three chromosomes of capillaris multiplied fourteen times. 

Marchal, whose work was done without knowledge of Rosenberg's 
paper, expressed (1920) the belief that four is the ground number of the 
genus Crepis. He noted that p.m.c. of a slightly aberrant capillaris plant 
had what appeared to be a large quadrivalent multiple chromosome 
plus two smaller but equal elements, and that most of the species of 
Crepis seemed to have four pairs of chromosomes. He therefore con- 
cluded that capillaris had arisen from the type by end-to-end union 
between two chromosomes. He believed that the differences in length 
which had been noted for C. lanceolata platyphylla (Tahara and Ishikawa, 
1911) could be accounted for by bipartition of one chromosome of a 
species with four pairs. He further suggested that six-pair species 
might arise by doubling of the three, and an eight-pair species by 
doubling of the four. He counted sixteen pairs for biennis and noted 
that, while the individual chromosomes in the p.m.c. of this species 
appeared somewhat smaller than those of certain four-chromosome 
species, the total mass was much greater. He then concluded that 
biennis is an eight-ploid species. 



MATERIAL AND METHODS 

A large number of species of the genus Crepis have been grown and 
identified in the greenhouse of the Division of Genetics of the University 
of California by Professor E. B. Babcock, thus making it possible to be 
certain of the specific determination of the material which was studied 
cytologically. Since the chromosome numbers which have been found 
to characterize the species thus identified differ in several instances from 
previously published counts, the data are presented in a convenient 
form in table 1. The root tips were fixed in chrom-acetic-urea and 
stained in Heidenhain's iron-haematoxylin. In most species the reduced 
number has also been counted by Belling's iron-aceto-carmine method. 



1925] Mann: Chromosome Number and Individuality in the Genus Crepis 299 



TABLE 1 

Chromosome Counts of 27 Species of Crepis 





Number 




Species 


N 


2N 


Author 


alpina L 


4 
5 


10 
10 


Marchal (1920)* 




Rosenberg (1920)f 
Mann (1922)J 


amplexifolia Willk 


4 


8 


Mann 






aspera L 


4 
4 


8 


Marchal (1920) 




Mann (1922) 


aurea (L.) Reichb 


5 


10 


Mann 






biennis L.. . 


16 
20 
21 
20 


40 


Marchal (1920) 




Rosenberg (1918) 
Rosenberg (1920) 
Mann (1922) 


blattarioides Vill... 


4 
4 


8 
8 


Marchal (1920) 




Rosenberg (1920) 
Mann 


breviflora Delile 


4 


8 


Mann 






bidbosa (L.) Tausch 


9 


18 


Mann 






bursifolia L. 


4 


8 


Mann 






capillaris (L.) Wallr 


3 


6 


Rosenberg (1909), Mann (1922) 






dioscoridis L 


4 
4 


8 


Marchal (1920) 




Mann (1922) 


foetida L 


4 
4 
5 


8 
10 


Marchal (1920) 




Rosenberg (1918) 
Mann (1922) 


grandiflora Tausch. 


4 


8 


Mann 






incarnata Tausch 


4 


8 


Mann 






japonica (L.) Benth. 


8 


16 


Tahara (1910), Mann (1922) 






myriocephala Coss. et D. R 


4 


8 


Mann (1922) 



* Marchal gives 1914 as the date of his counts, but they were not published until 1920. 
t Figured but not mentioned in the text. 

J Cited from Report of the College of Agriculture, University of California, July 1, 1921-June 30 
1922. 



300 University of California Publications in Agricultural Sciences [Vol. 

TABLE 1— (Continued) 





Number 




Species 


N 


2N 


Author 


neglecta L 


4 


8 


Rosenberg (1918), Mann (1922) 






palestina Boiss. Bornmuller 


4 


8 


Mann 


parviflora Desf 


4 


8 


Rosenberg (1918), Mann (1922) 


pulchra L 


4 


8 


Rosenberg (1920), Mann (1922) 


rubra L 


4 
5 


10 


Marchal (1920) 




Rosenberg (1918), Mann (1922) 


setosa Hall 


4 


8 


Mann (1922) 






sibirica L.... 


4 
5 


10 


Marchal (1920) 




Mann (1922) 


Sieberi Boiss 


6 


12 


Mann (1922) 






taraxacifolia Thuill 


6 

4 


12 

8 


Beer (1912) 




Digby (1914), Mann (1922) 


tectorum L.... 


4 


8 


Juel (1905), Mann (1922) 






vesicaria L 


4 


8 


Mann 



Table 1 shows that, while four is the most common haploid number 
for the twenty species studied, five is also fairly frequent. The other 
numbers (3, 6, 8, 9, and 20) are each represented by a single species. It 
is obvious that chromosome measurement should show whether cross- 
division, union into multiples, addition by non-disjunction, or combina- 
tions of these methods are sufficient to account for the differences in 
number found in the genus. It is also possible that hybridization 
between species with different chromosome numbers might account for 
the origin of certain cytological peculiarities. 

For some species the cytological material is far more abundant than 
it is for others, so that it is possible to measure only somatic metaphases 
in which all the chromosomes are fairly straight. The tendency of the 
long chromosomes of Crepis to twist is a source of considerable error 
where relatively poor material is available. The finest metaphase 
figures are to be found in the upper portion of the rapidly growing 
region of the root in seedlings, and in roots from adult plants. The 
region containing fine figures is greater in roots from the latter than 



1925] Mann: Chromosome Number and Individuality in lite Genus Crepis 301 

in the short root of the cotyledon stage, because there is a longer growing 
area in which the cytoplasm is less dense than it is at the tip, so that 
the chromosomes spread out more freely and the picture is less obscured 
by cytoplasmic inclusions. 

Table 3 is a compilation of measurement data for somatic metaphase 
figures in nineteen species of Crepis. In each case, except japonica 
and sieberi, ten somatic polar metaphases were drawn with a camera 
lucida. The magnification of the drawings is 4000 diameters. A 
moistened thread was placed along the center of the drawing of each 
chromosome, and then straightened and measured in millimeters. The 
figures were then placed in columns, the two largest in the first, and so 
on down to the two smallest. A sample of these records for a five- 
pair species, alpina, is given below in table 2. 



TABLE 2 

Actual Measurements of Drawings 



Differences from Average 



1 




2 


3 


4 


5 


Total 
Length 


1 


2 


3 


4 


5 


32 mm 


25 


mm 


14 mm 


13.5mm 


13mm. 














31 


27 




14 


13 


12.5 


195 mm. 


+5.8 


+5.7 


-0.5 


+0.4 


+0.8 


22.5 


20 




15.5 


13 


11.5 














24.5 


18 




14.5 


13 


11 


163 mm. 


-1.7 


-1.3 


+ 1.0 


-0.1 


-0.7 


30.5 


21 




17 


14.5 


12 5 














22 


19 




15 


14.5 


13 


179 mm. 


+4.3 


-0.3 


+2.5 


+ 14 


+0.8 


21.5 


17 




13 


12 


10.5 














23.5 


19 




13 


12 


11.5 


153 mm. 


-2.7 


-2.3 


-1.5 


-1.1 


-0.7 


23 


21. 


5 


16.5 


14 


12 














29 


20 




15 


12 


11.5 


174 mm. 


+2.8 


+0.2 


+2.0 


+0.9 


-0.2 



It is evident that even measurement by the rather crude method 
described above gives a fairly definite clue to the individuality of the 
species. It will also be noted that when the larger figure of each set 
is compared with the average for the chromosome, obtained by dividing 
the sum of the ten larger of the twenty chromosomes of one type by ten, 
the deviations for any one metaphase set are generally in the same 
direction (+ or — ). (See column headed "Differences from the 
average.") This deviation indicates that the error of measurement 
was not sufficient to conceal the fact that the chromosome lengths of a 
species maintain certain size relations at least throughout the later 
periods of shortening. It also shows that it is fair to use an average 



302 



University of California Publications in Agricultural Sciences [Vol. 2 



so obtained in a comparative study like this. The larger figure of 
each set was considered the more accurate measurement and hence 
was used to secure the 'corrected' totals and averages which appear in 
table 3. 

TABLE 3 
Measurement Data for Nineteen Species of Crepis 



Species 



C. capillaris 

C. neglecta 

C. setosa 

C. parviflora 

C. bursifolia 

C. aurea 

C. aspera 

C. alpina 

C. taraxacifolia 

C. tectorum 

C. blattarioides . . 

C. japonica a 

C. foetida 

C. bulbosa 

rubra 

dioscoridis 

sieberi a 

pulchra 

sibirica 



Hap- 
loid 

chromo- 
some 

number 


Cor- 
rected 
average 

total 
length 


3 


61.4 


4 


61.7 


4 


63.2 


4 


69.9 


4 


78.5 


5 


83.5 


4 


82.6 


5 


87.3 


4 


88.4 


4 


88.7 


4 


91.1 


8 


92.6 


5 


93.7 


9 


100.5 


5 


102.9 


4 


109.4 


6 


109.6 


4 


112.1 


5 


143.6 



Corrected average for individual chromosomes 



26.2 


20.4 


14.8 












24.5 


16.2 


11.2 


9.8 










22.3 


17.8 


14.0 


9.1 










25.3 


20.5 


14.4 


9.7 










24.3 


22.0 


19.5 


12.7 










21.0 


18.0 


16.2 


15.1 


13.2 








23.9 


21.5 


19.7 


17.5 










26.2 


21.3 


14.5 


13 1 


12.2 








26.1 


23.3 


21.2 


17.8 










28.1 


23.2 


20.2 


17.2 










29.0 


23.8 


20.6 


17.7 










15.7 


13.5 


12.2 


11.5 


10.8 


10.0 


9.7 


9.2 


25.0 


20.8 


17.7 


15.8 


14.4 








13.9 


12.8 


12.1 


11 7 


11.1 


10.6 


10.1 


9.6 


29.4 


23.9 


18.5 


16.2 


14.9 








35.9 


29.3 


24.9 


19.3 










26.8 


21.4 


17.7 


16.0 


15.2 


12.5 






36.7 


30.6 


25.5 


19.3 










41.9 


32.4 


27.6 


23.2 


18.5 









8.6 



a Averages from less than ten figures. 

The reliability of such measurements and the evidence for the 
constancy of specific individuality have been further corroborated by 
a study of chromosome measurements of the Fi's of two species-hybrids, 
setosa X tectorum (fig. 1) and setosa X dioscoridis (fig. 2). 1 It will be 
noted from table 3 that all three species involved have four pairs and 
that the chromosome sizes are far more different in the two latter than 
in the two former species. In both Fi's, however, it was possible to 
determine the source of the chromosomes by means of measurement 
data, and this was facilitated by the peculiar semidetached tip of the 
longest chromosome of setosa (fig. 3), by which it may usually be identi- 
fied. Since only one member of a set is present in each Fi figure, it 
seemed best to compare the averages for the Fi's with the uncorrected 
averages for the species involved. The results are tabulated below: 

1 For the use of these hybrids and the data on hybridization given below, I am 
indebted to Dr. J. L. Collins of this laboratory. 



1925] Mann: Chromosome Number and Individuality in the Genus Crepi-s 303 

TABLE 4 



setosa X dioscoridis 


39.9 


33.6 


28.9 


23 . 1 


22.1 
22.3 


18.1 

17.8 


13.7 
14.0 


10.3 


selosa 


9.1 


dioscoridis 


34.2 


28.9 


24.9 


20.6 
















+5.7 


+4.7 


+4.0 


+2.5 


-0.2 


+0.3 


-0.3 


+ 1.2 


selosa X teclorutn 


29.4 


24.1 


21.2 


16.8 


21.0 
22.3 


18.9 

17.8 


13.3 
14.0 


8.9 


setosa 


9.1 


lector um 


28.1 


23.2 


20.2 


17.2 
















+ 13 


+0.9 


+ 1.0 


-0.4 


-1.3 


+ 11 


-0.7 


-0.2 



The important point is that one can identify the chromosomes of 
dioscoridis and of tectorum by measurement when they are in combina- 
tion with those of setosa in an Fi hybrid, so that it is evident that the 
specific differences in length noted are not the product of interaction 
between a certain cytoplasm and its chromosomes. 

Since abundant material was available for capillaris (fig. 6), the first 
measurements, which were made on ten figures about as good as the 
average for all species, were checked by the use, first, of a mixture of 
slightly different metaphase stages (beginning to almost complete divi- 
sion) from a very short region of a single root tip, and, second, of a 
mixture from undivided figures from two different roots. These 
measurements show that averages for one chromosome in three different 
sets of ten from the same species may differ by as much as 3.55 mm., 
but that the averages give, in each case, very nearly the same differ- 
ences between the lengths of the different pairs. 



COMPARISON OF SPECIES 

Crepis neglecta (fig. 7) has a very characteristic individuality, two 
of the pairs being very similar and distinctly shorter than any of the 
chromosomes of capillaris. Its total length is very similar to that of 
capillaris, so much so that one is inclined to test the cross-division 
hypothesis for this species. If the two shortest averages are added, 
their sum is practically the same as the average for the intermediate 
chromosome of capillaris and the other average lengths are very similar. 



capillaris. 
neglecta.... 



26.2 
24.5 



20.4 
11.2+9.8=21.0 



14.8 
16.2 



■1.7 



+0.6 +1.4 



Attempts to cross the two species have as yet been unsuccessful. 



304 University of California Publications in Agricultural Sciences [Vol. 2 

Setosa (fig. 3), like neglecta, differs little from capillaris in total 
length. It contains, however, only one pair of chromosomes shorter 
than any in capillaris; otherwise it is rather similar to it. 

capillaris 26.2 20.4 14.8 

setosa 22.3 17.8 14.0 9.1 

-3.9 -2.6 -0.8 +9.1 

It has already been noted that the longest chromosome of setosa has 
a semidetached tip by which it may be recognized. This tip is usually 
at an angle to the main portion of the chromosome. In the figures 
given above the longest chromosome of setosa appears to have lost a 
portion of its length, while another pair of chromosomes averaging 
about ten units has been added. It is also possible that the longest 
chromosome has cross-divided, and that the peculiar chromosome of 
setosa really corresponds to the intermediate of capillaris. 

capillaris 26.2 20.4 14.8 

setosa 17.8+9.1=26.9 22.3 14.0 

+0.7 +1.9 -0.8 

If either of these possibilities represented the whole truth concerning 
the difference between the two species, we should expect reduction to 
be fairly normal following hybridization. As a matter of fact, no 
pairing occurs in the Fi setosa (N = 4) X capillar is (N = 3) (Collins and 
Mann, 1923), and as a consequence gametes are formed with 3, 4, and 
6 chromosomes as shown by five plants (backcrosses to setosa), which 
have 7, 8, and 10 somatic chromosomes. It seems possible that new 
types differing in number and combination of chromosomes may be 
obtained by selfing such plants as the backcrosses with ten chromosomes. 

Crepis parviflora (fig. 8) has a chromosome individuality much like 
that of setosa; the longer chromosome, however, averages slightly longer 
and does not appear to have a semidetached tip. 

setosa 22.3 17.8 14.0 9.0 

parviflora 25.3 20.5 14.4 9.7 

+3.0 +2.7 +0.4 +0.7 

It is evident that parviflora is more similar to capillaris than setosa, 
but like setosa it has an additional short pair of chromosomes. 

capillaris 26.2 20.4 14.8 

parviflora 25.3 20.5 14.4 9.7 

-0.9 +0.1 -0.4 +9.7 

The first hypothesis for setosa appears to be the more probable for 
parviflora. If it were true, one would have to account for the additional 
chromosome of 9.7 units by hybridization between two such forms as 



1925] Ahum: (.'hromtisnmc X umber and Individuality in the Genus Crepis 305 

neglecta and capillar is. The hybridization results for setosaX capillar is 
given above indicate that new types with new combinations of chromo- 
somes may arise in this manner. It will be interesting to observe the 
results of crossing setosa and parviflora. 

Bur si folia (fig. 9) appears to have an extra element of the size of the 
intermediate chromosome of the capillaris series: 

capillaris 26.2 20.4 14.8 

22 + 19.5 
bursifolia 24.3 =20.7 12.7 

-1.9 +0.3 -2.1 

It's average total length is 17.1 units longer than that of capillaris. 
Crepis taraxacifolia (fig. 10), tectorum (fig. 5), and blattarioides (fig. 
11) have very similar chromosome groups. 

taraxacifolia 26.1 23.3 21.2 17.8 

blattarioides 29.0 23.8 20.6 17.7 

tectorum 28.1 23.2 20.2 17.2 

All the chromosomes of these three species tend to average slightly 
larger than those of capillaris, but the differences do not greatly exceed 
those of the different averages for capillaris. If we suppose that the 
intermediate chromosome of capillaris has been duplicated in this 
group of species, the correspondence is somewhat bettered. 

Average of taraxacifolia, tectorum, and 

blattarioides 27.7 22.05 17.6 

Average of capillaris 26.2 20.40 14.8 

+ 1.5 +1.65 +2.8 

It is obvious that the relative lengths of the chromosomes in these 
three species are very similar to those in capillaris. 

Tectorum and capillaris were repeatedly crossed by Collins (1920), 
but the Fi developed only as far as the cotyledon stage. This indicates 
an incompatibility of the chromosomes or cytoplasm hard to account 
for on the basis of mere addition of similar material, especially when one 
considers that trisomic forms which come to maturity appear to be not 
uncommon among plants and animals. It will be very interesting to 
know whether others of the group of species indicated above will behave 
like tectorum in crosses with capillaris, and whether they will intercross. 

Aspera (fig. 12) is like the group discussed above except that the 
longest chromosome appears to be rather short. 

capillaris 26.2 20.4 14.8 

21 .5 + 19.7 

aspera 23.9 =20.6 17.5 

-2.3 +0.2 +2.7 



306 University of California Publications in Agricultural Sciences [Vol. 2 

Crepis bursifolia, taraxacifolia, tectorum, blattarioides, and aspera 
might all be derived from capillaris by duplication of the intermediate 
pair of chromosomes. 

The five-pair species listed below, although generally rather similar 
in chromosome individuality, show certain distinct differences. 

Total 
length 

aurea 21.0 18.0 16.2 15 1 13 2 161.9 

alpina 26.2 21.3 14.5 13.1 12.2 174.6 

foetida 25.0 20.8 17.7 15.8 14.4 187.4 

rubra 29.4 23.9 18.5 16.2 14.9 205.8 

Aurea (fig. 13) is outstanding since it lacks a long chromosome of 
about twenty-five units. The figures are excellent, so that the averages 
must be considered as very nearly accurate. Aurea is also very dis- 
tinctive morphologically. Alpina (fig. 14), foetida (fig. 15), and rubra 
(fig. 16) are much more alike in chromosome individuality. Alpina 
seems to have three pairs resembling the shortest chromosome of 
capillaris, and to be cytologically very like it otherwise. 

capillaris 26.2 20.4 14.8 

14.5 + 13.1+12.2 
alpina 26.2 21.3 — ' = 13.2 

+0.9 -1.6 

Foetida might also have three duplicates of the shortest chromosome 
of capillaris. 

capillaris 26.2 20.4 14.8 

17.7 + 15.8+14.4 
foetida 25.0 20.8 ■ ! = 15.9 

-1.2 +0.4 +1.1 

The figures for rubra compare better with those of capillaris if we average 
the two intermediates and the two shortest together. 

capillaris 26.2 20.4 14.8 

23.9 + 18.5 16.2 + 14.9 

rubra 29.4 -=21.2 - = 15.5 

2 2 

+3.2 +0.8 +0.7 

It was noted above that Rosenberg (1918) suggested that probably the 
small chromosome of capillaris had been duplicated twice for rubra. 
It will be seen from the figures that duplication of the intermediate 
and of the short chromosome appears more probable on the basis of 
the measurements presented here. 



1925] Mann: Chromosome Number and Individuality in the Genus Crepis 307 

Crepis japonica (N = 8) (fig. 17) and bulbosa (N = 9) (fig. 18) are 
rather similar in chromosome individuality, but are totally different 
from all the rest of the species studied in chromosome number and size. 

japonica 15.7 13.5 12.2 11.5 10.8 10.0 9.7 9.2 

bulbosa 13.9 12.8 12.1 11.7 11.1 10.6 10.1 9.6 8.6 

It is, of course, possible that japonica might have been derived from a 
species like tectorum by cross-division of every chromosome, or vice 
versa. When we test this hypothesis by adding the averages for the 
two largest, the next two, etc., of japonica together, the results are 

rather striking. 

15.7 12.2 10.8 9.7 

japonica | 13.5 11.5 10.0 9.2 

i 29.2 23.7 20.8 18.9 

tectorum 28.1 23.2 20.2 17.2 

+ 1.1 +0.5 +0.6 +1.7 

It is at least obvious that tetraploidy could not explain the chromosome 
individuality of japonica while cross-division might do so. 

Crepis sieberi (fig. 19) is the only species so far studied which has 
six pairs of chromosomes. It looks as if it might have four pairs of 
short chromosomes: 

capillaris 26.2 20.4 14.8 

17.7 + 16 + 15.2 + 12.5 

sieberi 26.8 21.4 — =15.3 

4 

+0.6 +1.0 +0.5 

or two intermediate and three short pairs: 

capillaris... 26.2 20.4 14.8 

21.4 + 17.7 16 + 15.2 + 12.5 

sieberi 26.8 ! =19.5 ! ! =14.6 

2 3 

+0.6 -0.9 -0.2 

Crepis pulchra (fig. 21) and dioscoridis (fig. 4) are very similar to 
one another in chromosome length. 

pulchra 36.7 30.6 25.5 19.3 

dioscoridis 35.9 29.3 24.9 19.3 

Difference 0.8 1.3 0.6 

C. sibirica (fig. 23), with five pairs, resembles pulchra and dioscoridis 
in choromosome measurements, and the average length of the two 
longest chromosomes, 36.5, indicates that it may have two instead of 
one of the longest type of chromosome. 



308 University of California Publications in Agricultural Sciences [Vol. '2 

41.9+32.4 

sibirica =37.1 27.6 23.2 18.5 

2 

dioscoridis 35.9 29.3 24.9 19.3 

Difference 1.2 1.7* 1.7 0.8 

If we suppose that this group of species has been derived from a 
type like capillaris, we must consider that the longest chromosome 
represents a multiple. If we subtract the intermediate average for 
capillaris (20.4) from the average of the longest chromosomes of all 
three species in this group (36.3), the remainder, 15.9, is only 1.1 units 
longer than the shortest chromosome of capillaris, indicating that an 
intermediate and a short chromosome might have united end to end 
to form an element averaging 36.3 units. Then if we average the two 
shortest chromosomes of these three species with the chromosome of 
20.4 units, which, we have supposed has united with a short element, 
the average, 19.9, is so like the intermediate of capillaris as to suggest 
that it may have been duplicated in the group under consideration. 
When we look at the averages now, the figures compare very well. 

capillaris 26.2 20.4 14.8 

pulchra, dioscoridis, ,> c i oq q_i_27 fi 

and sibirica —=29.1 19.9 15.9 

3 

+2.9 -0.5 +1.1 

These species obviously form a group by themselves, especially 
since it has been shown that the great size of the chromosomes in 
dioscoridis is maintained upon hybridization with a species like setosa. 



DISCUSSION 

For two reasons it is impossible to make any sweeping general- 
izations at this time concerning the data presented here. First, we do 
not yet know how species differing in chromosome number can arise, 
and second, we know too little about the genetics of Crepis. There are 
two known methods by which a single pair of chromosomes can be added 
to a complex, non-disjunction and species-hybridization, but in neither 
case has it been proved that stable types would ever result; and the 
formation of new species presupposes stability. It has. been suggested 
that it is very improbable that stability is to be expected of tetrasomic 
individuals because the complex as a whole is unbalanced by the addi- 
tion of chromosomes. This view seems to be borne out by observations 
on the cytology of tetrasomic plants of Datura (Belling and Blakeslee, 



1925] Mann: Chromosome Number and Individuality in the Genus Crcpis 309 

1924) and Matthiola (Frost and Mann, 1924). Both of those tetrasomic 
types are even feebler than the trisomic plants, and hence would have 
little chance of survival under unfavorable environmental conditions. 
The possibilities of species-hybridization as a source of differences 
in chromosome number within a genus are still less known. It might 
be argued with some plausibility that if a tetrasomic condition is 
unbalancing and associated with lessened viability, even less in the 
way of stability and viability should be expected of organisms having 
a pair of chromosomes from another species added to a complete specific 
complex. The Drosophila workers have found, however (Morgan, 
1922), that a similar genie structure characterizes the chromosomes of 
several species of that genus, and if this is true of Crepis, one method may 
be as probable as the other. It has been shown (Collins and Mann, 
1923) that new types with more chromosomes than either species 
possesses are formed when the Fi C. setosaXC. capillaris is backcrossed 
to setosa. It is only through further work on such types that the 
question of stability can be answered. The theoretical and practical 
value of such work is self-evident. 

While the little work that has so far been done on tetrasomic plants 
tends to show that they would be expected to be somewhat unstable 
genetically, tetraploid plants, e. g., Oenothera gigas, breed true. That 
Crepis biennis may be an octaploid from a five-pair species is indicated 
by the following experimental evidence : 

1. In the Fi C. setosaXC. biennis the twenty pairs of chromosomes 
from biennis form ten pairs. 

2. In the backcross of this Fi to biennis the thirty chromosomes 
from C. biennis form fifteen pairs. 

The great size and vigor which distinguish it from the other species 
studied also indicate that it is polyploid. The evidence from chromo- 
some measurements indicates strongly that Crepis biennis is the only 
one of the twenty species discussed in this paper that could owe its 
origin to polyploidy. 

It would seem possible that, if the whole complex of one species were 
added to that of another by segregation following species-hybridization, 
zygotes formed by the union of two such gametes might be expected to 
give stable races differing in chromosome number from other species 
of the genus. There is no evidence that such a procedure has occurred 
in any of the species of Crepis discussed above. 

There is at present little evidence that whole chromosomes can be 
lost and the resulting organisms be expected to give rise to new species. 
Genet ical and cytological results on Drosophila (Bridges, 1921) indicate 



310 University of California Publications in Agricultural Sciences [Vol. 2 

that while 53 per cent of the expected flies lacking one of the small 
fourth chromosomes live, they are imperfect, weak, and often sterile. 
That a small portion of a chromosome may be lost or inactivated is 
indicated also by work on this fly (Bridges, 1919). Loss of this strain 
is attributed to the injurious effect of the deficiency upon viability, 
fertility, and productivity. 

While loss of chromosomes appears to be somewhat improbable as a 
method by which one species can come to differ from another in chromo- 
some number, the chromosome number of some species may be reduced 
as a result of permanent end-to-end union of certain chromosomes to 
form multiples. The differences in number noted for the Acrididae 
(McClung, 1917) appear to be of this type. One species, Hesperotettix 
viridis, shows considerable variation in chromosome union in different 
individuals, indicating that it may be in the process of producing new 
types of chromosome grouping. It is also decidedly variable morpho- 
logically. 

There is some observational evidence that species differ from one 
another in chromosome number due to cross-division of all chromosomes 
of a complex. Marchal (1920), for example, reported that in the section 
Medium of Campanula the size of each chromosome of pollen mother 
cells is less when the haploid specific number is thirty-four than when 
it is seventeen. 

It is difficult to understand how cross-division or union of chromo- 
somes to form multiples could cause specific differences. In fact, a 
case from Drosophila reported by Mrs. Morgan (1922) indicates that 
while end-to-end union of the X-chromosomes may affect genetic 
results it has no effect upon specific characters. It seems simpler to 
suppose that such changes in chromosome complexes are the result 
rather than the cause of genetical differences between individuals, such 
as have been noted for Hesperotettix viridis and for the different species 
of the Acrididae. 

In the genus Drosophila, it has been shown that chromosomes that 
look alike may carry very different genes. For example, in D. willistoni, 
Metz and Lancefield (1922) report that the X-chromosome is a V- 
shaped element similar to the second and third autosomes of D. melano- 
gaster. Without this genetic evidence one would have said that these 
two species had the same type of chromosome complex. Such evidence 
is a timely warning to those who would draw hasty conclusions on the 
basis of data like those given above for Crepis. The genetical results 
from Crepis are still too scanty to permit of such tests. 



1925] Maim: Chromosome Number and Individuality in the Genus Crepis 311 



SUMMARY AND CONCLUSIONS 

1. With the exception of neglecta and possibly setosa, all the species 
of Crepis studied show significant increases in total length of the chromo- 
some complex over that of capillaris, the single species with three pairs 
of chromosomes. 

2. Generally speaking, increased number is associated with 
increased total length, but there are certain exceptions. 

3. In so far as studies on chromosome individuality can determine, 
five of the species with four pairs of chromosomes might have two 
pairs like the intermediate chromosome of capillaris. 

4. In Crepis neglecta (N = 4) the two shortest chromosomes might 
have been derived by cross-division of a chromosome of the length of 
the intermediate chromosome of capillaris. 

5. Crepis setosa (N = 4) and parvi flora (N = 4) are very similar in 
total length and quite unlike all of the other species. 

6. Crepis dioscoridis (N = 4) and pulchra (N = 4) have a long pair 
of chromosomes which is not represented in capillaris or in the other 
four chromosome species. It is possible that it might be a multiple 
chromosome. That this difference in length is not due to a difference 
in physiological condition or to error is shown by the fact that it is 
maintained when the dioscoridis chromosomes are in setosa cytoplasm 
in an Fi between these two species. All the chromosomes of these two 
species can be distinguished in this F x . 

7. Aurea stands out among the species with five pairs because of 
its lack of an element like the longest chromosome of capillaris. The 
complexes of rubra, foetida, and alpina might all have been derived by 
duplication of certain chromosomes of capillaris. Sibirica seems to 
possess two chromosomes like the large element of dioscoridis and 
pulchra. 

8. The single species with six pairs, sieberi, has chromosomes which 
are enough like those of capillaris in length to have been derived from 
it by chromosomal duplication. There appear to be but one pair 
of the large and the intermediate types, and four pairs like the short 
chromosomes. 

9. Japonica with eight pairs might be derived by cross-division of 
all chromosomes of a species like tectorum. 

10. Bulbosa (N = 9) has short chromosomes like those of japonica. 



312 University of California Publications in Agricultural Sciences [Vol. 2 

11. Biennis (N = 20) has chromosomes comparable in size to those 
of capillaris, and there is some experimental evidence which indicates 
that it is a polyploid from a five-pair species. 

12. It is well understood that these data are simply suggestive, 
but it is hoped that they may be of some use in taxonomic and hybridiza- 
tion studies on Crepis. The evidence, based on especially favorable 
cytological material, shows that it is entirely unsafe to assume that 
even closely related species which have the same chromosome numbers 
are identical in chromosome individuality; or to assume polyploidy 
unless the sizes of the chromosomes have been compared. 



LITERATURE CITED 

Beer, R. 

1912. Studios in spore development. II. On structure and division of the 
nuclei in the Compositac. Ann. Bot., vol. 26, pp. 705-726. 
Belling, J. 

1922. The cytology of Datura mutants. Carnegie Institute Year Book, vol. 

21, pp. 99-100. 
Belling, J., and Blakeslee, A. F. 

1924. The distribution of chromosomes in tetraploid Daturas. Am. Nat., vol. 
58, pp.. 60-70. 
Bridges, C. B. 

1919. Vermilion-deficiency. Jour. Genera] Physiology, vol. 1, pp. 645-656. 

1921. Genctical and cytological proof of non-disjunction of the fourth chromo- 
some of Drosophila melanogaster. Proc. Nat. Acad. Sci., vol. 7, pp. 
186-192. 

Collins, J. L., and Mann, M. C. 

1923. Interspecific hybrids in Crepis. II. A preliminary report on the results 

of hybridizing Crepis setosa Hall with C. capillaris (L.) Wallr. and 
with C. biennis L. Genetics, vol. 8, pp. 212-232. 

Digby, L. 

1914. Critical study of the cytology of Crepis virens. Arch. f. Zellforsch., 
vol. 12, pp. 97-146. 

Frost, H. B., and Mann, M. C. 

1924. Mutant forms of Matthiola resulting from non-disjunction. Am. Nat., 

vol. 58, pp. 569-572. 

JUEL, H. O. 

1905. Die Tetradenteilungen bei Taraxacum und anderen Cichorieen. Kungl. 
Svensk. Vetensk. Akad., Handl., vol. 39, no. 4. 
McClung, C. E. 

1917. The multiple chromosomes of Hesperotettix and Mermiria (Orthoptera). 
Jour. Morph., vol. 29, pp. 519-590. 
Marchal, E. 

1920. Recherches sur les variations numeriques des chromosomes dans la serie 

vegetale. Memoires de l'Acadcmie royale de Belgique, ser. 2, vol. 4, 
pp. 1-108. 



1925] Mann: Chromosome Number and Individuality in the Genus Crepis 313 

Metz, C. W., and Lancefield, R. 

1922. The sex-linked group of mutant characters in Drosophila willistoni. Am. 
Nat., vol. 56, pp. 211-241. 
Morgan, L. V. 

1922. Non-criss-cross inheritance in Drosophila mclanogaster. Biol. Bull., vol. 
42, pp. 267-274. 
Morgan, T. H. 

1922. Croonian lecture on the mechanism of heredity. Proc. Roy. Soc, Sec. 
B, vol. 94, pp. 162-197. 
Rosenberg, O. 

1909. Zur Kenntniss von den Tetradenteilungen der Compositen. Svensk. 

Bot. Tidskr., vol. 3, pp. 64-77. 
1918. Chromosomenzahlen und Chromosomendimensionen in der Gattung 

Crepis. Arch. f. Bot., vol. 15, pp. 1-16. 
1920. Weitere Untersuchungen liber die Chromosomenverhaltnisse in Crepis. 

Svensk. Bot, Tidskr., vol. 14, pp. 319-326. 
Tahara, M. 

1910. tlber die Zahl der Chromosomen von Crepis japonica. Bot. Mag., 

Tokyo, vol. 24. 



PLATE 53 



Somatic metaphases of Crepis species magnified 4000 diameters, using a B. and 
L. camera lucida mirror at 50, bar at 110, and a 1.8 mm. oil objective with an 18X 
Zeiss compensating ocular. Reduced in reproduction to 1800 diameters. 

F\ setosaXtectorum 

Fi setosaXdioscoridis 

setosa 

dioscoridis 

tectorum 



1. 
2. 
3. 
4. 

5. 
6. 

7. 



9. 
10. 
11. 
12. 



capillaris 

neglecta 

parviflora 

bursifolia 

taraxadfolia 

blattorioides 

aspera 



13. 


aurea 


14. 


alpina 


15. 


foetida 


16. 


rubra 


17. 


japonica 


18. 


bulbosa 


19. 


sieberi 


20. 


arrvplexifolia 


21. 


pulchra 


22. 


grandifolia 


23. 


sibirica 


24. 


biennis 



[314] 



UNIV. CALIF. PUBL. AGRI. SCI. VOL. 2 



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UNIVERSITY OF CALIFORNIA PUBLICATIONS 

IN 

AGRICULTURAL SCIENCES 

Vol. 2, No. 11, pp. 315-341, 7 figures in text March 6, 1926 



CHROMOSOME NUMBER AND INDIVIDUALITY 

IN THE GENUS CREPIS 
II. THE CHROMOSOMES AND TAXONOMIC RELATIONSHIPS 

BY 

ERNEST BROWN BABCOCK and MARGARET MANN LESLEY 



CONTENTS 

PAGE 

Introduction 315 

Material and methods 316 

Acknowledgments 316 

Taxonomy and cytology of twenty-one species of Crepis 317 

Literature and discussion 332 

Summary and conclusions 338 

Literature cited 339 



INTRODUCTION 

For the past three years we have been accumulating data on the 
taxonomy and cytology of the genus Crepis. The present paper repre- 
sents only two phases of our general project, which also includes exten- 
sive genetic research on species and species hybrids, the whole under- 
taking being an effort to establish a natural classification of a genus 
which has been a source of considerable difficulty to taxonomists and 
which presents a wide array of chromosome numbers. In addition to 
number we have examined the size of the chromosomes in the species 
studied, in the hope that this might also prove useful as a criterion 
in classification. 

We are confining our discussion to species which we have been able 
to cultivate in the greenhouse or garden and to identify with certainty, 
a procedure which has thrown considerable light on the classification. 
Ideally the taxonomist should know his species as they appear under 
natural conditions, but obviously this is impossible for any one botanist 
in the case of such a large and widely distributed genus as Crepis. 



316 University of California Publications in Agricultural Sciences [Vol.2 

But, even though field studies of most of the species could not be made, 
it was yet necessary to cultivate them in order to study them eyto- 
logically, and hence it has been possible to supplement the examination 
of herbarium material by observations on cultivated plants which were 
grown under fairly uniform conditions. By this method it has been 
possible to show that certain characters (for example, nodding position 
of the young flower heads) which have been used by some authors to 
separate sections of the genus, are variable within a single species. 

Crepis was chosen in the first place because certain species have 
small chromosome numbers and because the chromosomes are compara- 
tively easy to study in some detail. A previous paper on chromosome 
size and number in the genus (Mann. 1925) contained a majority of 
the chromosome data herein considered, together with a suggestion as 
to how a cytologist would be tempted to group the species studied. In 
this paper we have added somewhat to the cytological data and have 
attempted to utilize both the cytological and the taxonomieal modes of 
attack. Generally speaking, this method has proved of the greatest 
usefulness; and. while certain irreconcilable situations still appear to 
exist, we have reason to hope that future developments — as we obtain 
more species and make further studies — may show how such situations 
have arisen and lead the way to a (dearer understanding of the genus. 

MATERIAL AND METHODS 

The species of Crepis upon winch this study is based are all from 
the Old World, and have mostly been obtained through the cooperation 
of European botanists. Since we desire to make our study as complete 
as possible, we shall greatly appreciate any assistance towards obtain- 
ing viable s Is in- roots of additional species. The taxonomic studies 

have included the examination of both dried and living specimens, and 
much care has been exercised in the determination of all this material. 
The cytological methods were described in Mann (1925). 

Acknowledgments 

The investigations herein reported were conducted in part through 
an allotment from the Adams Fund. It is with pleasure that we 
acknowledge the assistance of Dr. J. L. Collins and Mr. C. W. Haney 
in the growing of cultures and in providing us with certain data on 
species hybridization. All the drawings were made by Helen E. 
Rearwin, whose attention to accuracy of detail is gladly acknowledged. 
Our thanks are also due to the curators of herbaria and directors of 



1926] Bdbeoek— Lesley : Chromosomes and Taxonomic "Relationships 317 

botanic gardens in numerous institutions. Many taxonomic and other 
treatises on the Compositae have been consulted, which cannot be cited 
in this brief paper. 

TAXONOMY AND CYTOLOGY OF TWENTY-ONE SPECIES 

OF CREPTS 

In the present paper we do not wish to discuss the taxonomy of 
Crepis in detail or to propose any taxonomic revision of the genus, but 
merely to set forth the general features of the group and its sub- 
divisions in such a way as to enable the reader to appreciate some of 
the difficulties involved in attempting to classify the species according 
to a natural system. Also, it is hoped that the significance of the cyto- 
logical data herein presented will be clearer after a preliminary con- 
sideration of the outstanding morphological resemblances and differ- 
ences to be found within this group of plants. 

No thoroughgoing investigation of the entire genus has been made.. 
Some of the species have been studied since the time of Linnaeus or 
even earlier, and at least forty-four other generic names have been 
applied by twenty-four authors in attempting to classify various por- 
tions of the assemblage. The purposes of the present paper can be 
best served by a discussion of the treatment of the genus given by 
Hoffmann in Engler and Prantl's Pflanzenfamilien. This treatment, 
represented in condensed form below, includes all but six of the twenty- 
one species for which complete data as to chromosome size are avail- 
able and one other (C. patula) which Ave have not yet been able to 
secure. The six species referred to — blattarioides Vill., bursifolia L., 
neglecta L., parviflora Desf., montana d'Urville, and setosa Hall. f. — 
are all easily placed in Hoffmann's categories with the exception of 
neglecta, which is referred to Eucrepis in most recent floras (see p. 
327). A translation of Hoffmann's description of the genus is given 
below "for the information of readers who are not familiar with this 
groups of plants. His analysis of the genus and key to the sections 
appear in table 1. 

Crepis L. — Heads small to rather large, yellow- or seldom recb 
flowered, borne singly or in panicles of variable form ; involucre cylin- 
drical or bell-shaped, often with loose or appressed outer calyx, the 
inner fructiferous bracts often becoming stouter and harder through- 
out or along the middle nerve ; receptacle naked or ciliate ; fruit 10-30 
ribbed, with a short callosity on the base, reduced or beaked at the 
apex, the outer fruits sometimes shaped differently from the inner 
ones ; pappus in most species composed of soft pliable hairs, seldom 
somewhat brittle and brownish, in the marginal fruits sometimes lack- 
ing. — Herbs, very seldom half-shrubby plants. Perhaps 170 species 
mostly from the northern hemisphere. 



318 University of California Publications in Agricultural Sciences [Vol. 2 





a a- 

Fig. 1. Achenes of Crepis alpina — a, marginal; a', inner. X 7 circa. 



L'JiliiJ Bab cock-Lei It y : Chromosomes and Taxonomic "Relationships 319 





Fig. 2. Marginal and inner achenes of: b, b', Crepis rubra; c, <•', C. foetidu. 

X 7 circa. 



320 University of California Publications in Agricultural Sciences [Vol. 2 



TABLE 1 

Hoffmann 's Key to the Sections of Crepis with the Addition of Six Species 
Not Listed by Him and References to Original Drawings of Achenes 

A. Pappus bristles very short, unequal, the longest scarcely as long as the width 

of the fruit, very readily deciduous; fruit short-beaked. 

Sec. I. Ceramiocephalum Schultz Bip.* 
C. patula Poir. 

B. Pappus bristles longer. 

(a) Inner or all the fruits long-beaked. 

Sec. II. Barkhausia Much.* 

Fruits all beaked (outer sometimes shorter than inner), involucre 
mostly with outer calyx, seldom imbricate. Fig. 1, a, a' ; Fig. 3, d, 
e, e' g, g'. 
C. alpina L., turaxaci folia Thuill., bursifolia L., setosa Hall. f. 
Sec. III. Anisoderis Cass.* 

Outer fruits short-, inner long-beaked. Fig. 2, b, b', c. <■'. 
C. foetida L., rubra L. 
Sec. IV. Nemauchenes Cass* (in part). 

Marginal fruits not or scarcely beaked, enclosed within the 
much hardened involucral bracts; ribs prominent, the innermost 
enlarged wing-like so the fruits seem to be compressed; inner 
fruits prismatic long-beaked. Fig. 3, h, h' . 
C. aspera L. 

(b) Fruits reduced at the apex, but not beaked or only short-beaked. 

Sec. V. Nemauchenes Cass.* (in part). 

Except for the scarcely beaked inner fruits, like TV. Fig. 4, 
k, I'. 
C. Dioscoridis L. 
Sec. VI. Cymboseris Boiss.* 

Marginal fruits compressed, 3-angled, the edges winged, enclosed 
by the inner much hardened involucral bracts, without pappus. 
Fig. 4, m, m' , m". 
C. palaestina Boiss. (Boriim.). 
Sec. VII. Phaecasium Cass.* 

Fruits alike in shape with readily deciduous pappus which is 
mostly absent in the marginal fruits, inner fructiferous involucral 
bracts much hardened. Fig. 4, ft, ft', n". 
C. pulchra L. 
Sec. VIII. Aetheorrhiza Cass.* 

Distinct from others by tuberous root-stock, fruits all similar 
in shape. Fig. 6, «. 
C. bulbosa (L) Tausch. 

Sec. IX. Eucrepis DC. 

Roots not tuberous (fusiform or root-stock as though bitten 

off); fruits all alike; involucre with outer calyx; inner fructiferous 

involucral bracts mostly moderately thickened. Fig. 5, o, p, q, r, s, t. 

C. capillaris (L) Wallr., neglecta L., parviflora Desf., tcctorum L., 

biennis L., montana d'Urv. 

* Described as a genus. 



1 * * — * > J Babcock-Lesley: Chromosomes and Taxonomic Relationships 321 

Sec. X. Youngia Cass.* 

Distinct from preceding section in the small few-flowered (8-15) 
heads. Stem few-leaved; involucre in mature fertile heads little 
changed. Pappus readily deciduous. Fig. 6, v, v'. 
C. japonica (L) Benth. 

Sec. XI. Catonia Much.* 

Involucre imbricate, often black hairy; outer bracts shorter 
but at least half as long as inner bracts and forming no distinct 
outer calyx, in mature fertile heads flat and unchanged. Fig. 6, 
w, x,; fig. 7, y. 
C. sibirica L., aurea (L) Cass., blattarioides Vill. 

We shall first discuss Hoffmann's grouping of the twenty-one 
species now before us, and then suggest a more natural grouping, in 
order that the cytologic data to be presented may be more intelligently 
considered. It will be noted that the genus, as treated by Hoffmann, 
is divided into three subgenera but without designating them as such. 
The first consists of the monotypie section, Ceramiocephalum ; the 
second (a) contains three sections all characterized by having fruits 
with definite beaks; and the third (?>), comprising the remaining 
seven sections, contains species none of which have manifestly beaked 
fruits. It was long ago pointed out (Bischoff, 1851) that all degrees 
of development of the beak are found in group (a), while some of the 
species included in group (b) have fruits with very short or obscurely 
developed beaks. But this seems to be generally looked upon as 
merely part of the evidence of relationship within the whole group 
and as part of the argument for treating it as a single genus. 

Section I is set apart from all the other species, probably justifiably. 
but, as we have not yet been able to work with living material of this 
interesting species, it is unnecessary to give it further consideration 
at present. 

Subgenus (a), on the basis of fruit characters alone, would be 
better rearranged as follows: 

Sec. II. Fruits large, the inner ones 10-18 mm. long. 

C. alpina, foetida rubra (cf. figs. 1 and 2). 
Sec. III. Fruits small, all alike, the inner ones 5-8 mm. long. 

C. bursifolia, setosa, taraxacifolia (cf. fig. 3, d, e, g). 
Sec. IV. Fruits small, of two shapes, marginal ones winged. 

C. aspera (cf. fig. 3, h, h'). 

Furthermore, the above rearrangement is not inconsistent with 
other morphological characters of diagnostic value. This is especially 
interesting in connection with the cytological evidence, the species 



* Described as a genus. 



322 



University of California Publications in Agricultural Sciences [Vol. 2 



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324 University of California Publications in Agricultural Sciences [Vol. 2 

grouped under Section II all having 5 pairs of chromosomes of similar 
size, while those under Sections III and IV have 4 pairs but differ 
somewhat in individuality. It is worthy of note that one character 
commonly used in distinguishing between these species, viz.. the posi- 
tion assumed by the young flower heads before anthesis. whether erect 
or nodding, has been found to be too variable in the case of foetida to 
make it of diagnostic value. 

In its dimorphous fruits, the inner ones beaked and the outer ones 
winged, C. aspire exhibits relationship with Barkhausia on one side 
and the Diascoridis group on the other (cf. fig. 4. 1c, A'). Its chromo- 
some group resembles those of the three Barkhausia species in having 
chromosomes of medium size, and it has been crossed with two of these 
species. But these hybrids exhibit very abnormal reduction phe- 
nomena, whereas hybrids between certain Barkhausia species (vesi- 
caria, MarscJxdlii and taraxacifolia) show normal pairing and reduc- 
tion. Thus all the evidence indicates that aspera belongs in a class by 
itself. Furthermore, ampleocifolia, which closely resembles aspera 
morphologically, also has 4 pairs of medium-sized chromosomes 
(p. 331). 

Subgenus (b) is a heterogeneous group which is scarcely capable 
of satisfactory classification on the basis of fnih characters alone. 
Thus in the case of sections V, VI, and V 1 1 there is much stronger 
affinity, as indicated by comparative morphology, than would appear 
from Hoffmann's synopsis. In all three of the species concerned the 
inner involucral bracts of fructiferous heads are conspicuously thick- 
ened or much hardened. Then, too, palaestina has a combination of 
some of the distinguishing characters of the other two species, and 
yet it is in no sense an intermediate form such as mighl arise from 
hybridization. The flower heads in palaestina are large and showy. 
and the marginal fruits are enclosed within the inner involucral bracts, 
in these respects resembling Diascoridis, while the inner fruits bear a 
strong resemblance to those of pulchra. Furthermore, the fruits in 
pulchra, contrary to Hoffmann, are sometimes of two distinct shapes, 
the marginal ones being flattened as in palaestina ( cf. tig. 4). Without 
going into further details at this time, we may suggest that these three 
sections might Avell be combined into one. The chromosome groups 
of pulchra (N = 4), palaestina (N = 4), and Diascoridis (N = 4) 
are indistinguishable, and the F 1 of pulchra X palaestina is highly 
fertile. 

Section VIII, Aetheorrhiza, must stand alone, at least for the 
present. While the inflorescence of bulbosa suggests strong relation- 



1920] Bab cock-Lesley: Chromosome* and Taxonomic Eelationships 



325 



3 

TO 



►3 



p 

9 

CIS 



H3 



'a 






3 





S. <" 




326 



University of California Publications in Agricultural Sciences [Vol.2 



ship with a urea, this species is cytologically very different from all 
other species of Crepis, having 9 pairs of short chromosomes. The only 
species studied which it at all resembles in tins respect is japonica. 
which has 8 pairs of chromosomes of similar size. 




Fig. 6. Typical achen.es of: u, Crepis bulbosa; v, C. japonica — v', cross-section 
outline; w, C, anna; x, ('. blattarioides. X 6.5 circa. 

Section IX. Eucrepis, contains six of our twenty-one species, and 
on the basis of fruit characters alone (cf. fig. 5) they comprise three 
groups, as follows: 1. capillaris and parviflora; 2. neglecta, tectorum, 
montana; 3. biennis, lint if we consider habital and other morpho- 
logical characters, they may be rearranged as follows: 1. capillaris, 
parviflora, neglecta; 2. tectorum; 3. biennis; 4. aiontana. Such an 
arrangement is of interest when considered in relation to the chromo- 
somes of these species. It was noted (Mann, 1925) that the total 
length of the chromosome group in capillaris (N = 3) is practically 
the same as that of neglecta (N = 4), while parviflora (N = 4) appears 
to have a short chromosome added to a complex like that of capillaris. 
The chromosome group of tectorum (N=4) could not be differentiated 



19261 



Bdbcock— Lesley : Chromosome* and Taxonomic Relationships 



327 




-V 



Fig. 7. Typical achene of: y, Crepis sibhica. X 7 circa. 

from that of taraxacif olia in Barkhausia, but biennis (N = 20) and 
montana (N = 6) stand apart from all other species from the stand- 
point of chromosome number. 

It should be observed that C. neglecta has long been a troublesome 
species to students of this difficult genus. In the Genera Plantarum 
(Bentham and Hooker, 1873) neglecta is considered as intermediate 



328 University of California Publications in Agricultural Sciences [Vol. 2 

between Eucrepis and Lagoseries (Barkhausia) ; parviflora was given 
similar intermediate status, but this is manifestly an error. In the 
Flora Orientalis (Boissier, 1875) we find a statement which we trans- 
late as follows: "As the achenes gradually diminish into a short beak, 
it is doubtful whether this species belongs in Eucrepis or Barkhausia; 
it affords a connecting link between the two sections." Boissier places 
it under Barkhausia, presumably because the young flower heads 
assume a nodding position. The unreliability of this character has 
been pointed out. Moreover, recent taxonomists (e.g., Fiori, 1904) 
have placed neglect a in Eucrepis, where it seems to belong rather than 
in Barkhausia, as its fruits are variable in shape and even when they 
are beaked the beak is very short, as shown in figure 5g. 

Section X, Youngia, is represented here by only one species, but 
contains several others, of which one is fuscipappa (p. 331). These 
comprise a very distinct group in certain morphological characters, 
insomuch that some authors have suggested placing it in Lactuca. 
But it is claimed (Bentham and Hooker, 1873; Hooker, 1882) that the 
species of this group (except two referred to Lactuca or Ixeris) 
resemble Eucrepis more closely than Lactuca, and that japonica, which 
is the type species of Cassini's genus, Youngia, does not differ much in 
floral characters from C. parviflora, a statement which is partially 
true, although a number of differences do exist. Tt was noted above 
that japonica (N = 8) resembles bulbosa in having very short chromo- 
somes. It is the only species knuwn in the genus with 8 small chromo- 
somes (japonica chromosomes total about 93 units in length as com- 
pared with 137 for fuscipappa) and it was shown in Mann (1925) 
that considering chromosome size alone it might have been derived 
from tectorum (Eucrepis) by cross-division of all chromosomes. How- 
ever, these two species are so widely different morphologically that 
such a derivation seems hardly possible. On account of the strongly 
flattened fruits in japonica. (cf. fig. 6, v. v'), together with the other 
differences noted in Hoffmann's key and the small size of the chromo- 
somes, one may advocate the recognition of Cassini's Youngia as a 
genus intermediate between Crepis and Lactuca. Cassini (1831) in 
the original diagnosis of Youngia states: "fruits oblong, more or less 
flattened, . . . absolutely beakless" . . . [genus] "not to be con- 
founded with Crepis because of the flattened fruits." Further com- 
parative study of shape of fruits and size of chromosomes will be 
necessary, however, before a final conclusion can be drawn. 



1920) Babcock-Leslcy : Chromosomes and Taxonomic Relationships 329 



TABLE 2 

Tentative Classification of Twenty-one Species of Crepis, Arranged for 
Comparison with Hoffmann's Classification Shown in Table 1 

B. Pappus bristles longer. 

1. Inner or all the fruits long-beaked. 

2. Fruits large, the inner ones 10-18 mm. long. 
See. II. Anisoderis. 

C. alpina, foetida, rubra (figs. 1 and 2). 
2*. Fruits small, the inner ones 5-7 mm. long. 
3. Fruits all similar. 
See. III. Barkhausia. 

C. bursifolia, sctosa, iaraxacifolia (fig. 3, d, e, g). 

3*. Fruits of two shapes, the marginal ones winged. 
Sec. IV. Nemauchenes. 
C. as per a (fig. 3, h, h'). 
1*. Fruits reduced at apex, but not beaked or only short-beaked. 

4. Inner involucral bracts conspicuously thickened or hardened in 
fructiferous heads. 
Sec. V. (Gatyona, Cymboseris, Phaecasium.) 
C. Dioscoridis, palaestina, pulchra (fig. 4). 

4*. Inner involucral bracts not much thickened or hardened in fructi- 
ferous heads. 
5. Inner involucral bracts more or less spongy-thickened dorsally. 
Sec. VI. Eucrepis. 

C. capillaris, parviflora neglecta, tectorum, biennis, montana (fig. 5). 
5*. Inner involucral bracts little or not at all changed. 
6. Heads small, florets few, small. 
Sec. VII. Youngia. 
i, C. japonica (fig. 6, v, v'). 

6*. Heads large, florets numerous, large. 

7. Plant short-stemmed, scapigerous, scapes 1-headed, rarely 
2-3 headed. 
8. Rootstock stoloniferpus, forming tubers. 
Sec. VIII. Aetheorrhiza. 
C. bulbosa (fig. 6, u.) 

8*. Rootstock simple, non-tuberous. 
Sec. IX. Omalocline. 
( C. aurea (fig. 6, w). 

7*. Plant long-stemmed, erect, foliate. 
Sec. X. Soyeria. 

C. sibirica, blaitarioides (fig. 6, x; fig. 7, y). 

Section XI, Catonia, is defined by Hoffman as including species 
of at least two distinct groups, Omalocline Cass, and Soyeria Mann., 
represented among our species by aurea on the one hand and by 
blaitarioides and sibirica on the other. In other words, he has used 
an ill-defined genus (Moench, 1794) as a catchall for species not 
already assigned to sections. This would be more evident if we were 
considering a larger number of species. Furthermore, blattarioides 



( 



330 



University of California Publications in Agricultural Sciences [Vol.2 



and sibirica, although somewhat similar in both habital and fruit 
characters (see figs. 6. 7), are very distinct from each other in many 
respects and have the same general native and distributional habitats, 
all of which would indicate that they are not closely related species. 
The three species of Catonia studied differ greatly cytologically. 
Aurea (N = 5) is rather different in individuality from the other 
species with 5 pairs. Blattarioides (N = 4) has a chromosome group 
much like that of tectorum, while sibirica has ."> pairs of very large 
chromosomes resembling those of Dioscoridis, puichra, and palaestina. 
Three other species in this section have been counted recently, but as 
no measurements have yet been made, they arc not included in table 3 
(see p. 331). 

TABLE 3 

Tabulation of Twenty-one Species of Crepia A.cc6rding to a Tentative New 

Taxonomic Grouping and with Reference i<> Ni mber and Length of 

Chromosomes. (The Lexuth Values Represent Averages 

from Tex Differext Cells.) 



Number of Chromosome Pairs 



Sec. II Anisoderis 

nl inn, i 
ioi tula 
rubra 
Sec. Ill Barkhausia 

bursi folia 
8< tOSQ 

taraxacifolia 
Nemauchenes 



S,T IV. 

Sec, V.* 
Sec. VI. 



Sec. VII 
Sec. VII 
Sec. IX. 
Sec. X. 



aspera 



Dioscoridis 
palaestina 
puichra., 
Eucrepis 
capillaris 

parviflora 

tectorum 

montana 

'</• iinis 

Youngia 
japonica -. 
I. Aetheorrhiza 

bulbosa 

Omalocline 

a an a 

Soyeria 

sibirica 
blattarioides. 



26 
25 
29 

.'I 
22. 
26 l 

23 '.< 

35 (i 
:u l 
36.7 

26.2 

2.-, :i 

28 I 

26.8 
(20 

15.7 

13.9 

21 

41.9 
29.0 



21.3 
20.8 
23.9 

22.0 

17 8 
23 :i 

21 :, 

29.3 

27 I) 
30.6 

20.4 
20 ."■ 
23.2 
21.4 

13 ■"> 

12 8 

18.0 

32.4 
23.8 



1 1 7. 
17 7 

is :, 

in ;. 

i i n 

21 2 

19.7 

24.9 
24.6 

2.". :> 

I 1 8 
It I 
20.2 

17 7 



12 2 

12 1 

16.2 

27.6 
20.6 



13. 1 

l.-, 8 

16 2 

12 7 
'.'. 1 

17 s 

1 7 :» 

19 3 
21 2 
19.3 



17.2 
16.0 



11.5 

11 7 
15. 1 

23.2 

17 7 



12 2 

1 1 I 

1 I 'i 



I A . 2 

10.8 

II 1 
L3 2 

is :, 



12 .". 

Ill (I 
1(1 (', 



9.7 

Id 1 



'.I 2 
9.6 



S li 



*Gatyona, Cymboseris, and Phaecasium combined. 

t Not measured; size range much like that of species in this group. 



L926] 



Bdbcock— Lesley : Chromosomes and Taxonomic Relationships 



33] 



Our analysis of relationships among these twenty-one species, as 
based on comparative morphology, is summarized in table 2. This 
analysis is presented only in a tentative way, as an aid in the study of 
eytologicaJ evidence and a step toward the classification of the entire 
genus. 

The correspondence of the new taxonomic grouping with chromo- 
some number and size is shown in table .'{. 

Since the foregoing was written, the chromosomes have been 
examined in the following additional species of Crepis. The classifica- 
tion into sections is according to the tentative new arrangement shown 
in tables 2 and 3. 

IV. Nemauchenes 
C. amplexifolia (Godr.) Willk N= 4 size medium 

VI. Eucrepis 

C. hjrata Froel N= 6 size medium 

C. mollis (Jacq.) Asch N= 6 size medium 

C. pygmaea L N= 6 size medium 

C. chondrilloides Jacq N= 4 size large 

C. Blavii Asch N= 4 size large 

C. ciliata C. Koch N = 20 size medium 

VII. Youngia 

C.fuscipappa (Thw.) Bent ,h N= 8 size medium 

IX. Omalocline 

C. Hookeriana Ball N= 4 size medium 

X. Soyeria 

C. conyzaefolia (Gouan) Dalla Torre N= 4 size large 

C. tingilana Salz. ex Ball N= 5 size medium 

C. paludosa (L) Mnch N= 6 size large 

With reference to the six species classified under Eucrepis, the first 
group of three lyrata, mollis, and pygmaea, must be grouped with 
montana on the basis of morphology, and they have similar chromo- 
somes. The next two, chondrilloides and Blavii, represent a subdivision 
of Eucrepis not previously studied and are very distinct from other 
members of Eucrepis. Lastly ciliata is certainly in Eucrepis, and its 
chromosomes indicate relationship to biennis, to which species there is 
considerable resemblance in the rosettes of our immature plants. 
Evidently Eucrepis is too heterogeneous a group to be retained as a 
section, and in the taxonomic revision of the genus which is now in 
preparation it will become a subgenus containing several sections. 



332 University of California Publications in Agricultural Sciences [Vol. 2 

It is evident that, generally speaking, there is a definite correspond- 
ence between the taxonomic position of the species studied and their 
chromosome number and especially with chromosome size, and that the 
new taxonomic grouping increases this correspondence. It is almost 
perfect in Section II, and in Section III (cf. table 3), and the species 
that stand apart in the classification also differ markedly from the rest 
in either size or number of chromosomes (Sections V. VI, and VII). 
It will be noted that Section III and Section VI contain species 
will) similar chromosome numbers and sizes, parviflora and setosa 
having very similar size differences, as do also twraxacifdlia and 
tectorum. It would seem worth while to test these groups by means 
of species-hybridization. Sections VII and VIII as compared with 
Sections V and X exhibit the most extreme differences in chromosome 
size. 



LITERATURE A XI) DISCUSSION 

The numerous summaries of chromosome numbers which have 
appeared in recent years clearly indicate that there is some parallelism 
between chromosome number, size, and shape and relationship in the 
plant and animal kingdoms. In general, members of the same genus 
usually have similar chromosome numbers. In the Liliaceae, for 
instance, each genus has a characteristic number of chromosomes. On 
the other hand, in wheat, instead of exact numerical correspondence 
within the genus, the species fall into three groups with respect to 
chromosome number (Sakamura. 1918), einkorn having 7, emmer 14. 
and vulgare 21 pairs of chromosomes. These groups also differ from 
one another in susceptibility to rust, serological relations, and 
morphology (Sax, 1921). Thus in the genus Triticum the most similar 
species are most alike in chromosome number. Winge (1!)17, pp. 166- 
168) cites an interesting case from the Compositae. Species were 
described as having 8, 9, 14, 16, 18, 24, 27, 32, 36, and 4."> pairs. When 
these species were classified by tribes, the numbers formed two series 
with 8 as the ground number for the Ileliantheae. and 9 for the 
Anthemideae. Marchal (1920) recently noted that the species of the 
genus Campanula which belong to the section .Medium have X values 
of 17, 34, or .31, but finds that the other section of the genus fails to 
show a similar numerical seriation, including such X values as 8, 10. 
and 13. He suggests (p. 66) that "The results of the cytological study 
of species of section II [Rapunculus] tend to show that this grouping 
is much less natural and less homogeneous than the preceding." 



1920] Babcock— Lesley : Chromosomes and Taxonomic "Relationships 333 

McClung (1908), on the basis of observations on many genera of 
Orthoptera, says, 

Merely as :i result of the study I have made of the germ cells I would have 
classified these insects into two groups, one having a complex of twenty-three 
chromosomes and the other of thirty-three. On the other hand, many taxo- 
nomists, from careful and minute examination of the external anatomy of these 
same species, had agreed in placing them into family groups which they call 
the Acrididae and Locustidae. 

McClung (1917) has made an especially thorough study of the genera 
Hcsperotettix and Mermiria, and lias had the benefit of the cooperation 
of experts on the classification of the Orthoptera, with similar results. 

Metz (1914, 1916) has shown that the Drosophilidae have rather 
similar chromosomes and that the species form several groups on the 
basis of their cytological characteristics. Metz and Lancefield (1922) 
state that the 13 species belonging to class A, of which D. melanog aster 
is an example, are scattered throughout the genus. The Drosophilidae 
are of especial interest from the standpoint of cytology and taxonomy, 
since something is known of the arrangement of genes within the 
chromosomes of several species, and it is therefore possible to com- 
pare the chromosomes from a genetical as well as a purely morpho- 
logical viewpoint. Sturtevant (1921) says, "44 recessive mutant 
genes in 41 loci of D. melanogaster and 12 recessive mutant genes 
of D. simulans (in 12 loci) are also recessive in melanog aster-simulams 
hybrids." Some of these genes are found in each of the 4 chro- 
mosomes indicating that "The data from D. simulans show what 
was suggested by the other results and by much cytological data, that 
the constitution of a chromosome may be essentially the same in two 
different species. ' ' Both of these species belong to type A cytologically 
(Metz and Moses, 1923) and are closely related taxonomically. The 
evidence from I), obscura and D. willistoni, on the other hand, shows 
that the chromosomes which one would naturally suppose to be 
identical on the basis of purely cytological criteria are not the same 
genetically, since Metz and Lancefield (1922) state: "In the two 
species having V-shaped X chromosomes, then, yellow and scute are 
'located' near the middle of the chromosome map, while in melano- 
gaster with its short rod-like X chromosome, yellow and scute are on 
one end." Metz and Moses (1923) emphasize the importance of 
genetical evidence in any attempt to evaluate the significance of 
similarities or differences of a cytological type. 

Lists of chromosome numbers also contain what appear to be many 
flagrant exceptions to the view that the species of a genus will be cyto- 



334 University of California Publications in Agricultural Sciences [Vol.2 

logically similar. In fact, the summaries of Ishikawa (1916) and 
Tischler (1916, 1922) contain very few genera with either the same 
number throughout, or even a single ground number. Even in the 
Liliaceae certain species have been reported as having chromosome 
numbers different from that typical of the genus. Time and further 
work alone will tell how many of these exceptions are real and how 
many are due to error. At present few genera have been much studied, 
and even where a large number of counts have been published, the same 
error may appear in a whole series of observations. For instance, in 
both Triticum and Rosa numerous species were included in recent 
summaries as having 8 and 16 pairs of chromosomes. Il has been 
shown by Sakamura (1918) and Sax (1918, 1921) for Triticum, and 
by Tiickholm (1922) for Rosa, that 7 and not S is the ground number 
for both genera. Another very real source of error in any attempt to 
generalize from summaries lies in the fact that few eytologists are 
trained taxonomists. Our experience with Crepis indicates thai seeds 
which are obtained from the most reputable sources may be incorrectly 
labeled, and, unless the seeds are grown and the plants classified, we 
cannot always be positive that they even belong to that genus, much less 
to the species to which the sender has attributed them. While lists of 
chromosome numbers include such errors as are indicated above and 
are, therefore, not suitable as a basis for very sweeping generalization, 
no one can doubt that chromosome number and. in some cases, size and 
shape, are good specific characters. We venture the prediction that 
chromosome number and size will sometime lie given with taxonomic 
descriptions. 

Crepis contains species with 3. 4. 5, 6, 8, 9, and 20 pairs of chromo- 
somes; but 3, 6, 8, 9, and 20 are much less frequent numbers than 4 
or 5, each of the former characterizing only one of the twenty-one 
species represented in table 3. A similar condition has been described 
for a closely related genus, Lactuca (Ishikawa, 1921), most of the 
species having 5, 8, 9, or 12 as the haploid number, while single species 
have 7, 16, or 24. It is especially interesting that Ishikawa finds that 
his grouping of species according to chromosome number and size cor- 
responds very strikingly with the taxonomic classification of Nakai 
(1920). In Lactuca, as in Crepis, great differences in chromosome 
size exist, and because of this and the numerical differences, Ishikawa 
is inclined to think that Lactuca is really an assemblage of genera. 
It is particularly interesting that two varieties of L. dentata have 12 
pairs, while one has 7 pairs of chromosomes. 



1926] Bdbcock— Lesley : Chromosomes <nt<t Taxonomic Relationships 335 

Crepis senecwides Delile, a native of Egypt, is a species of peculiar 
interest because its fruit is definitely flattened, although not so much 
so as in the more extreme types of Lactuca, and it lacks the thin lateral 
margin (fig. 3, /, /'), while on the basis of its involucre, number of 
florets per head, and habit it does not fit into any of the sections of 
Lactuca provided by Hoffmann in the Pflanzenfamilien. Further- 
more, it has four pairs of small chromosomes and produces sterile 
hybrids when crossed with C. parvifiora and C. vesicaria. Thus we 
find fairly close relationship between what simulates Lactuca in achene 
shape and certain species of Crepis. This evidence is not unique, how- 
ever, as there are other points at which the two genera meet. Nakai. 
for example, found it necessary to choose between the alternatives of 
either recognizing Ixeris, Paraixeris, and Crepidiastrum as distinct 
genera or combining Crepis and Lactuca. For the present, we are 
inclined to consider C . senecioides as Crepis, but it is highly desirable 
that critical comparison of the fruits be made between senecioides and 
similar Crepis species as well as between senecioides and the North 
African species of Lactuca, and that chromosome counts of the latter 
be obtained. We have indicated one such comparison in the drawing 
of C. bursifolia (fig. 3, g, g'). 

A group of forms which have usually been treated as distinct 
species, viz., Crepis vesicaria L., C. ta/raxadfolia Thuill., C. Marschallii 
F. Schultz, and C. myriocephala Coss. et DR., may be considered as 
one species for the following reasons: (1) They are closely similar 
morphologically, and their close relationship has been recognized by 
several taxonomists. (2) They have nearly identical chromosome 
groups. (3) They intercross freely and produce highly fertile hybrids. 
That these should be considered as subspecies of one species rather than 
as varieties is indicated by the following facts: (1) All except one. 
taraxacifolia, which is probably the oldest phylogenetically, occupy 
distinct geographic areas. (2) All are highly variable, and taraxaci- 
folia is really polymorphous. However, as no changes in nomenclature 
are proposed in the present paper, we shall continue to use the 
binomials in what follows. 

A summary of the data recently presented by Bleier (1925) and 
Karpetchenko (1925) shows that in Trifolium section Chronosemium* 



* Greene (1897) discusses at length the evidence for retaining the genus 
Chrysaspis instead of treating it as a* section (Chronosemiiun) of Trifolium. 
He says: ''And since Linnaeus' time there have been a number of open protests, 
and by most able botanists, against the treating of the Hop Trefoils as con- 
generic with such plants as Trifolium pratense and its allies. Systematists of 
no less renown than Lamarck and Desfontaines referred the plants to Melilotus 
rather than Trifolium." 



336 Universitj/ of California Publications in Agricultural Sciences [Vol. '2 

contains species with 7 or 14 pairs of chromosomes, while Enamoria 
and Galearia consist of species with 8 or 16 pairs, except for T. 
glomeratum which has 7 pairs; whereas Lagopus contains species with 
7, 8 or a large number of pairs, possibly 48-49. Bleier presents some 
evidence that differences in nuclear volume and in chromosome size 
occur in the genus. The cases of Trifolmm, Campanula, Lactiica, and 
Crepis are alike in that, while many correspondences have been found 
between chromosome number and classification, some exceptions still 
exist which require further study. Even within Eucrepis, however, 
which shows a remarkable diversity of chromosome numbers, morpho- 
logical resemblances appear within the section which are correlated 
with similarity of chromosome number and size. 

In the genus Seneeio, At'zelius (1924) reports a high degree of 
homogeneity within the genus as indicated by close conformity to the 
numerical series, 5, 10, 20, 30; also in most of the sections, ;is only one 
of the eight sections contains species of different numerical rank. 
However, as the species he lias studied are mostly from the Old "World, 
the situation within the genus as a whole may yet be found to differ 
considerably. 

In Carex, Heilborn (1924) has recently reported thai species exist 
with 9, 15, 16, 19, 24, 26, 27, 28, 29, 31, 32, 33, 34. 35, 36. 37, 38, 40. 
41, 42. and 56 as haploid numbers. Related species show some num- 
erical similarity, although this is by no means so striking as in Lactuca. 

('reins also contains a series of chromosome numbers like that 
reported for Carer, 3, 4, 5, 6, 8, 9, and 20 pairs. Most of the species 
with 3, 4, 5, 6, and 20 pairs have chromosomes similar in size, although 
some 4- and 5-paired species have chromosomes that are much larger 
than is usual in Crepis, in so far as it has been studied cytologically. 
Two of the three species which we have found with S and 9 pairs 
have much smaller chromosomes than is usual in the genus. It was 
noted above that the section Youngia might be removed from Crepis. 
If this is done we shall lack species with 8 pairs. It is noteworthy 
that Eucrepis contains species with 3, 4, 5, 6, and 20 pairs. Navashin 
(1925&) and Collins and Mann (1923) found evidence that polyploidy 
occurs in Crepis, but it was pointed out by Mann (1925) that some 
other type of chromosome multiplication must account for the origin 
of most of the species which we have studied. Non-disjunction was 
first suggested as a source of the chromosome differences observed by 
Rosenberg (1918) ; and, whereas this cannot account for all the differ- 
ences, it may be the most important factor. In any case it certainly 



-\ 



l!i2(i| Bab cock—Lesley : Chromosomes and Taxonomic Relationships 3.37 

is the most probable method which we know occurs. Tt should be 
emphasized in all such discussion, however, that there is no known case 
of a stable combination of chromosomes which has been observed to 
originate in this way. Similarly, no case of changed individuality of 
the chromosomes which would account for stable types like C. setosa, 
neglecta, and parviflora has been reported to have occurred experi- 
mentally. Chromosome fragmentation is known to occur following 
trisomy, but whether such types ever become stabilized with a pair of 
fragments added to the normal specific complex, or whether a chromo- 
some complex can lose a considerable section of a pair of chromosomes 
and the plants lacking this part be viable and fertile, is unknown. Our 
strain of C. MarschaJlii is peculiar in that, when we obtained it, certain 
plants contained 9 chromosomes in the root-tip cells, comprising the 
usual complex for the vesicaria group of species plus a very short 
unpaired chromosome. The source of this small extra chromosome is 
quite uncertain, although it is known to be an addition to the complex. 
Navashin (1925) presented a figure of C. Marschalh'i that is like 
vesicaria and lacks the small chromosome. Some of our 9-chromosome 
MarschaJlii plants were very fertile, and among their progeny one at 
least has two such small chromosomes. This matter is being studied 
further and will be reported upon separately. Should such a plant be 
fertile, we might understand how such differences in chromosome 
groups could arise in a genus. 

Navashin (192;k/) has emphasized the importance of minute 
"Traibanten" or satellites attached to the tips of certain chromosome 
pairs in Crepis species. He believes that shape of chromosome and the 
presence or absence of satellites is "weit wichtiger fur die Charakter- 
istiJe des Kernes bzw. der Art, als die Zahl der Chromosomal u nd deren 
Dimensioiien siud." He groups together in class " D " all chromosomes 
having satellites although in C. Dioscoridis, one of 19 length units bears 
the satellite, while in C. parviflora: he finds it upon one of about 10 
length units. But in our material, which was fixed in C. A. U., 
Trabanten were not always present, and sometimes resembled the 
strands and masses of nucleolar material which are frequently found 
being extruded from the chromosome plate. Consequently size, which 
is relatively far less variable and more easily evaluated, was selected 
as the best criterion of relationship, and it has thus far proved a very 
good one as tested by species-hybridization. That shape relationships 
may help in differentiating two pairs of chromosomes of the same size 
in certain species of Crepis is clearly indicated by Navashin 's figures, 



338 University of California Publications in Agricultural Sciences [Vol. 2 

but the relative importance of size and shape as indicators of relation- 
ship between species can be tested only by species-hybridization and 
genetic analysis. Probably both modes of attack will sometime prove 
useful, but thus far they have not given us clues to relationship which 
could not be determined by comparative length alone. Our' material, 
like that of Navashin, shows Trabanten attached to the shortest chro- 
mosome in both tectorum and Marsckallhi, species which are widely 
separated in all classifications. This is very disappointing, since one 
might have hoped that they could be differentiated thereby. It seems 
evident from our studies that if Navashin were to make comparative 
measurements of the chromosomes, he might change his estimate of the 
chromosome homologies in the species which he studied. 

Corrections in Nomenclature in Part I 

In the preceding paper (Mann, 1925), the following corrections 
should be made : 

For breviflora Delile read senecioides Delile. 

For grtmdiflora Tausch read cony zae folia (Gouan) Dalla Torre. 

For Sieberi Boissier read montana d'Urville. 



SUMMARY AND CONCLUSIONS 

1. Taxonomically considered, the genus Crepis, as it stands at 
present, is a heterogeneous assemblage of distinct but related groups of 
species. The sections recognized by Hoffmann and their classification 
by him are not wholly satisfactory on the basis of comparative morph- 
ology alone. A more satisfactory classification of the species under 
consideration, which reduces the sections from eleven to ten and 
regroups certain species, is suggested, and the cytological evidence is 
considered in relation to the new grouping. 

2. From the standpoint of cytology as well, the genus Crepis must 
be considered as heterogeneous. Similarity of chromosome size seems 
to be a better criterion of relationship than number alone, although 
closely related species usually have the same numbers of chromosomes. 
Most of the cytological heterogeneity is confined to the sections 
Eucrepis and Catonia of Hoffmann's classification. The former is 
found to be too heterogeneous both taxonomically and cytologically 
to be retained as a section, and certain new subgroupings are needed 
within it. Catonia also requires some drastic changes. It is hoped 
that further study will reveal natural subgroups within Catonia; also 



1926] Babcock— Lesley: Chromosomes and Taxonomie Relationships 339 

1 luit it may throw light on the origin of chromosomal differences in 
Crepis. Further research on species hybrids is in progress and should 
throw considerable light on problems of relationship within the genus. 

3. Differences in chromosome dimensions are found among the 
species of this genus. We note especially (a) differences in size of all 
the chromosomes; (b) similarity in size of most of the chromosomes 
and differences in others. If Youngia be omitted, there remains only 
one species, C. bulbosa, having all the chromosomes smaller than is 
usual for the genus. At present we have this species in a section by 
itself, but its ultimate classification awaits further study. Of the three 
species of type (6), in which certain chromosomes are much shorter 
than is usual in the genus and the others are similar in size, C. negiecta 
and C. parviflora are provisionally classified in Eucrepis, while C. 
setosa is in Barkhausia. 

4. It is noted that certain species having similar chromosome sizes, 
particularly C. tectorxim and the vesicaria group (including taraxaci- 
folia, Marsrhallii, and myriocephala) , are classed respectively in 
Eucrepis and Barkhausia. These facts may indicate either close 
relationship between the two sections or that similar changes in the 
chromosomes have taken place independently in the two groups. For 
the present we favor the latter assumption. 

5. This study was undertaken partly for the purpose of testing the 
cyto-taxonomic method in a genus favorable for such research. As the 
work progresses we are becoming more and more impressed with the 
value of this method, and it is our intention to extend it to include 
as many species of Crepis as can be obtained and cultivated at 
Berkeley. 

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